Harper, 73, tells People magazine that she has leptomeningeal carcinomatosis, a rare condition that occurs when cancer cells spread into the fluid-filled membrane surrounding the brain.

Doctors say she has as little as three months left to live. Harper received the devastating news on Jan. 15.

“I was stunned,” Harper says of receiving the diagnosis. “And in the next minute I thought, ‘This could draw more attention to cancer research.’ I think there’s an opportunity to help people.”

“I don’t think of dying,” she tells People in the exclusive cover story. “I think of being here now.”

“Don’t miss your life,” Harper adds.

Harper previously battled lung cancer in 2009.

The TV star is best known for playing neurotic New Yorker Rhoda Morgenstern, Mary Richards’ sidekick in the classic sitcom “The Mary Tyler Moore Show” (1970-1977). Harper then starred in the successful spin-off, “Rhoda,” from 1974 to 1978.

“I’m absolutely devastated by this news,” Mary Tyler Moore said to People. Harper called her former co-star the day before she went public with her illness.

“Valerie has given so much joy, laughter and love to the world,” Moore, 76, continued. “I join her fans and send much love and positive thoughts to her and her family during this difficult time.”

Following Wednesday’s shocking announcement, actor Jason Bateman, who played Harper’s son on the ’80s sitcom “Valerie,” also issued a message of support to his former TV mom.

“Valerie is someone that I’ve learned a great deal from. Not just comedically but also in her ability to put whomever approached her, or worked with her, completely at ease with a laugh and an energy that’s intoxicating,” the “Arrested Development” star said in a statement to “Entertainment Tonight.”